Apparatus for cooling granular material

ABSTRACT

A continuous system for cooling hot granular material comprising a treatment chamber having upwardly extended sidewalls formed of electrically insulating material and an inlet and outlet. Means is provided for moving the material from the inlet toward the outlet during the cooling process and water supply means is provided for adding moisture to the material in the chamber for evaporative cooling of the material. Means is provided for regulating the water supply means to control the rate of water added to the material in response to the condition of the incoming material, and the regulating apparatus includes at least one pair of sensing electrodes which are mounted on the insulating sidewall of the chamber for sensing the moisture condition of the granular material in the chamber. The addition of moisture from the water supply means is regulated in response to the detected moisture condition.

United States Patent 3,256,573 6/1966 Hunter 241/110 3,395,834 8/1968 Troy 222/63 3,456,906 7/1969 Troy 241/47 Primary Examiner'-Edward C. Allen Attorney-Mason, Kolehmainen, Rathburn & Wyss I the condition of the incoming material, and the regulating apparatus includes at least one pair of sensing electrodes which are mounted on the insulating sidewall of the chamber for sensing the moisture condition of the granular material in the 2,824,282 2/1958 Posey 259/154 chamber. The addition of moisture from the water supply 2,863,191 12/1958 Dietent et a1. 259/154 means is regulated in response to the detected moisture condi- 2,954,215 9/1960 Warmkessel 259/154 tion. 1

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SIGNAL CONTROLLED SWITCHING DEVICE llO INVZSN'I'UR. ELBERT C. TROY ATT'YS APPARATUS FOR COOLING GRANULAR MATERIAL The present invention relates to a new and improved continuous system for cooling hot granular material, such as foundry sand and the like, and is an improvement on the apparatus shown and described in the copending US. Pat. application Ser. No. 547,824, filed May 5, l966,assigned to the same assignee as the present invention,- now US. Pat. No. 3,456,906.

In the past, many attempts have been made to provide a continuous system for the cooling of hot foundry sand, and the like, as the sand becomes available from a mold shake-out station in the foundry. Batch-type coolers have been employed with some success; however, in a batch-type cooling operation, it is usually necessary to wait until a sufficient amount of material has accumulated in the foundry shake-out operation before the batch is processed in order to have any reasonable chance of obtaining uniform characteristics of temperature and moisture content in the material after cooling. Batch-type systems are inefficient in that the cooling apparatus is often idle for long periods of time between batches, and a skilled operator is neededto oversee the operation in order to obtain a reasonable degree of uniformity in the characteristics of the finished material. v

One of the problems which makes it exceedingly difficult for a continuous type of cooling system to operate within workable limits of uniformity of sand temperature and moisture characteristics is the factthat in typical foundries the mold shake-out operation is not necessarily run on a continuous basis and the volume flow rate of sand available from the shake-out station is intermittent and fluctuates widely, depending on the production of the foundry itself. Also, wide variations in sand temperature and moisture content are encountered, making it even more difficult to cool the sand on a continuous basis and obtain the desired degree of uniformity in the finished product.

In the copending US. Pat. application, Ser. No. 547,824,

previously mentioned, a suitable apparatus for use in a continuous system is disclosed and claimed, and this apparatus has met with considerable commercial success in foundry operations. U.S. Pat. No. 3,395,834, filed May 4, i966 and issued Aug. 6, I968, also assigned to the same assignee as the present invention, is directed to a discharge door and control system for use in a continuous-type cooling system, and this refinement provided another step forward in producing a continuous system for cooling of hot granular sand as it is received from a foundry shake-out station.

. The present invention is a further refinement or improvement on the apparatus of the aforementioned copending applications and has met with considerable success in foundry operations;

in the cooling system of the present invention, moisture is added to the incoming sand in the mixing chamber for evaporative cooling thereof. The flow rate of moisture added is controlled by an electric sensing system developing a signal proportional to the electrical resistance, and thus the wetness of the material in the mixing chamber. This signal is used to regulatethe amount of moisture added to thematerial so that thematerial or finished product discharged from the chamber has a workable degree of uniformity iii-moisture content and temperature regardless of the variations in characteristics and flow rate of the incoming material. A low resistance of the material in the chamber indicates a relatively high water content and lower temperature and, accordingly, the amount of moisture-addedfor cooling is reduced, while a high resistance of; ,the material indicates relatively low temperature and moisture content and an increase inthe flow rate of added moisture; is provided to achieve the desired degree ofevaporatiye cooling in thecooling process to obtain uniform results in thefinal: product. Because'theflow of material to the cooling system isintermittent and fluctuates widely in flow rate, in order toinsure that ample material is present in.the chamber to obtain an accurate evaluation of the moisture content and temperature of the incoming material, the present invention provides means for maintaining a minimum level of material in the mixing chamber before the moisture control system is put into operation.

It is therefore an object of the present invention to provide a new and improved system for cooling granular material on a continuous basis. i

Another object of the present invention is to provide a new and improved continuous system for cooling granular material of the character described wherein widely fluctuating flow rates of material into the system can be tolerated and yet reasonably uniform characteristics of temperature and moisture content in the final product are obtained.

Another object of the present invention is the provisionv of a new and improved continuous system for cooling granular material wherein the moisture added for evaporative cooling of the material is regulated in flow rate in accordance with the wetness of the material itself.

Another object of the present invention is the provision of a new and improved system for cooling granular material on a continuous basis wherein the walls of the cooling chamber are formed of insulating material and a plurality of electric sensing probes for sensing the resistance of the material are mounted at conveniently appropriate locations on the wall.

Another object of the present invention is the provision of a new and improved continuous system for cooling granular material of the type described wherein the flow rate of moisture added to the material for evaporative cooling thereof in.the cooling chamber is regulated in accordance with the condition of the material, thereby providing more uniform characteristics of temperature and moisture content in the material or finished product discharged from the system.

Another object of'the invention is to provide a new and improved continuous system for cooling hot granular material including means for regulating the level of material in the cooling chamber for insuring'that accurate sensing or measurement of the moisture content and temperature is achieved, resulting in more uniform characteristics in the material discharged or leaving the system.

Another object of the present invention is the provision of a new and improved control means for regulating the water flow in response to the condition of the material in the cooling chamber whereby a minimum amount or level of material in the chamber is required before the water control system is put into operation, thereby insuring the uniform quality of material discharged from the system.

The foregoing and other objects and advantages of the present invention are accomplished in one illustrative embodivelocity, cooling airflow directly into the material as it is moved around the cooling chamber during the cooling process. Water supply means is provided for adding a controlled amount of moisture to the material in the chamber for evaporating cooling thereof, and means is provided for regulating the water supply means including at least one pair of electrodes which are mounted on the insulating sidewall of the chamber to detect the resistance of the wetted material in the chamber. A signal developed by the electrodes responsive to the wetness or dryness and thus the temperature of the material, controlsand regulates the amount of moisture added to the material'through the water supply means.

For a better understanding of the present invention reference should be' had to the following detailedd'escription whentaken in conjunction with the drawings, in which:

FIG. 1 is a vertical, sectional view of a new and improved apparatus for cooling hot granular material'and characterized by the featuresof the present invention;

FIG. 2 is an enlarged, fragmentary, sectional view illustratsidewall for. directing sensor current treated in the apparatus;

FIG. 3 is an elevational view of the conductive front face of the electrode taken substantially along lines 3-3 of FIG. 2;

FIG. 4 is a block diagram of the moisture control system of the apparatus for regulating the amount of moisture added in the cooling process; and 1 FIG. 5 is a schematic diagram of the electrical circuit of the moisture control system.

Referring now, more particularly, to the drawings, therein is illustrated a new and improved apparatus for cooling hot, granular material constructed in accordance with the features of the present invention, and referred to generally by the reference numeral 10. The cooling apparatus is generally referred to hereinafter as a mixer or cooler and is adapted to receive hot granular material, such as foundry sand, from a belt conveyor 12, which receives sand from one or more mold shake-out stations in the foundry wherein the castings are removed from the mold flasks and the sand is separated out.

through the material The hot'granular material from the belt conveyor 12 is introduced into the mixer 10 through an inlet hopper or surge chamber 14, positioned at the upper end of a downwardly extending inlet chute 16, the lower end of which is open and centered above a rotating mixing head assembly 18. The mixing head 18 is mounted for rotation about a vertical axis adjacent one end ofa large, generally rectangulan'mixing chamber 20 having a rectangular bottom wall 22 supported from the floor or other surface on a plurality of upstanding legs 24.

The mixing chamber 20 includes an outer, vertical, peripheral sidewall 26 having a horizontal flange or rim 28 fastened along the upper edge of the sidewall and an inner sidewall 30 formed of rubber or other flexible, electrically insulating material and sloping downwardly and inwardly from the flange 28 and secured to the bottom wall 22, as shown in detail in FIG. 2. The upper edge portion of the sloping flexible insulating sidewall 30 is secured to the flange 28 by means of a peripheral rim or dumping plate 32 which is bolted to the flange,.sandwiching the upper edge portion of the flexible, innersidewall between the plate and flange. As best shown in FIG. 2, the lower edge portion of the flexible, insulating sidewall is secured to the bottom wall 22 .of the mixing chamber by a lower clamping bar 34 having a rod 36 welded along the inner end thereof and bolted to the bottom plate 22 by a plurality of bolts 38, thereby sandwiching the flexible sidewallf30 between the bar 34 and the bottom wall 22, holding it tightly in place.

I The sloping inner sidewall 30 is thus supported along its upper and lower edge portion under tension so that the wall is in a taut condition and is deflectable inwardly and outwardly relative to the central portion of the chamber 20 as the material is thrown outwardly against the wall by rotation of the mixing head assemblies. Because the sloping inner sidewall 30 is formed of flexible, insulating material, such as sheet rubber, or the like, the mixing chamber 20 may be constructed in a generally rectangular shape with sharp corners, and because of the rebounding action of the wall, the material is thrown inwardly toward the central portion of the chamber into the paths-traversed by the'mixing heads. The rebounding flexible wall construction is more fully described and is claimed in the aforementioned copending Pat. application, Ser. No 547,824, and results in a lower fabrication cost for the apparatus because no curved or rounded corner wall surfaces are required.

As best shown in FIG. 1, an air plenum chamber 40 is defined around the mixing chamber 20 between the flexible inner sidewall 30, the upstanding vertical outer sidewall 26- and the outer peripheral edge portion of the bottom wall 22. Cooling air for the material in the chamber is supplied to the plenum chamber through an inlet duct 42 connected to a blower or fan 44 driven by an electric motor 46. When the fan 44 is operating, a large volume of cooling air is supplied to the ing one of the electrode means on the mixing chamber,

plenum at a pressure of l to 3 p.s.i., and the cooling air is injected inwardly'directly into the material within the mixing chamber 20 through a plurality of cross-shaped openings or slits 48 located around the lower edge portion of the inner sidewall 30. The air passes through the opening at high velocity for cooling the material in the chamber and, because the inner wall 30 is constructed of flexible material, the crossshaped openings 48 are easily formed by merely cutting slits in the material itself at any desired location. The high velocity air from the plenum chamber 40 passes through the slits or openings 48 and is directed into'the material contained in the lower portion of the chamber, thereby effecting highly efficient cooling of the material.

The cooler 10 also includes a second mixing head assembly 50 rotatable about a vertical axis parallel with and spaced from the axis of rotation of the inlet mixing head assembly 18. The mixing head assemblies 18 and 50 are driven to rotate in opposite directions, as showy by the arrows in FIG. 4, and each includes a plurality of radially extending, horizontal plow support anns 52 which are supported at their inner ends by a turrethead 54. The turrethead 54 are mounted on the upper ends of vertically extending drive shafts 56 which project downwardly through spaced openings in the bottom wall 22 of the mixing chamber 20. Cylindrical collars 58 are provided around the shafts 56 to prevent material from engaging the shafts and entering hearings 57 mounted in the bottom wall 22 for supporting the shafts. Each of the mixing head assemblies 18 and 50 includes a plurality of sloping plow members 60 which are mounted on support legs 62 supported from the outer ends of the radial'arms 52 of the mixing heads. Each plow 60 and leg 62 is adjustable on its respective radial arm 52 so that the clearance between the lower edge of the plow and the bottom wall 22 and between the outer edge of the plow and the sidewall 30 ofthe mixing chamber 20 can be adjusted and set as desired. As the mixing heads 18 and 50 rotate, as shown in FIG. 3, the plows 60 engage the material in the chamber, moving it rapidly around the chamber, and the high velocity cooling air injected from the plenum chamber 40 through the slits or cross openings 48 passes directly into the agitated and moving granules of the material to provide efficient cooling. The material first entering the mixing chamber 20 through the feed chute 16 is engaged by the mixing head assembly 18 and is later transferred to the second or final mixing head assembly 50 for eventual discharge through a discharge opening 64 (FIG. 4) in the side of the chamber. The discharge opening is controlled by means of a pivotally mounted discharge door 66 which is automatically controlled and is more fully described in the aforementioned U.S. Pat. No. 3,395,834. Opening and closing of the door 66 are effected by a door control cylinder 68 in a manner whereby a desired minimum level of material is maintained in the mixing chamber 20 at all times during operation.

Power for driving the shafts 56 of the mixing head assemblies l8 and 50 is supplied by an electric drive motor 70 through a pair of belt drives 72 connected to gear reducers 74 which are directly connected to the lower end of the drive shafts 56 by couplings 76. As more fully described in the aforementioned copending U.S. Pat. application No. 547,824, an electrically operated door controller 78 (FIG.'4) is provided to operate a pair of solenoid valves 80 in compressed air lines 82 and 84 connected to the opposite ends of the door cylinder 68. Compressed air from a suitable source, such as a compressor, is supplied to the control valves 80, and when either one of the valves is open air is fed to one of the respective cylinder supply lines 82 or 84 for operation of the door cylinder to open or close the discharge door 68. The door controller 78 provides operating current for the respective valves 80 through electrical lines 86 and 88, and the operating current opens the valves in response to the current being drawn by the drive motor 70 which is responsive to the amount of material in the chamber 20. Motor current flows, through lines 70a, 70b, and 700, and one or more current transformers 90 are provided to sense the amount of current flowing to the drive motor 70 and an electrical signal in response thereto for input to the door controller 78 through input leads 92.

When the level of material in the mixing chamber is relatively low or below the desired minimum, the horsepower supplied by the drive motor 70 and, correspondingly, the current drawn through the lines 70a, 70b, and 700 are relatively low.

' The current transformers 90 sense the low level of power being supplied and an appropriate signal is fed through the input leads 92 to the door controller 78. The door controller responds to the low level signal by sending an output signal through the line 86 to open the valve 80 in the air line 82. Pressurized air is thereby supplied to the outer end of the door cylinder 68 causing the discharge door 66 to move toward the closed position. When the door begins to close, the discharge rate of material is reduced and the level of the material in the mixing chamber 20 begins to build up to a higher value. As this occurs, the current drawn by the drive motor 70 rises correspondingly until the output signal supplied to lead 86 is extinguished and the valve 80 in the air line 82 is closed. When the level of material in the mixing chamber 20 is above the desired operating level, the signal input to the door controller 78 from the transformers 90 and input lines 92. results in a signal being initiated through the control lead 88 to open the valve 80 in the air line 84. When air is supplied to the door cylinder through line 84, the door 66 begins to open and increasevthe rate of discharge of the material from the mixing chamber 20, thereby lowering the level of material correspondingly. The control system thus maintains a relatively constant level or height of material in the chamber 20 even though the flow or input of material changes from time to time and is sometimes intermittent. As more fully described in the aforementioned U.S. Pat. No. 3,395,834, when the level of material in the chamber 20 is between desired upper and lower limits, both of the valves 80 in the respective lines 82 and 84 are closed and opposite ends of the cylinder 68 are vented to the atmosphere so that the door 66 is in a free floating intermediate range. The door control system is provided with means for selectively adjusting the upper and lower limits and, appropriately, a low-set indicator needle A, a high-set indicator needle B, and an instantaneous indicator needle C are provided therefor.

In summary, and as described in the aforementioned U.S.

Pat. No. 3,395,834, the discharge door 66 is automatically controlled by means of the door controller 78 and associated components to maintain a desired level or range of height of material in the mixing chamber at all times, even though the flow rate of material into the mixing chamber through the inlet chute l6 varies widely and is intermittent. In accordance with the present invention, water is supplie to the material in the chamber for evaporative cooling thereof through a ringlike water supply manifold 100, which is positioned directly above and in concentric relation with the inlet mixing head assembly 18. Cool water, supplied to the material in the chamber from the inlet manifold 100, is used for evaporative cooling of the material and the interaction of the high velocity airflow injected through the openings 48 in the wall 30, together with the evaporationof the moisture added by the water manifold, results in the highly efficient cooling of the hot granular material until it reaches to the desired temperature range. The evaporative cooling process taking place in the mixing chamber 20 results in the production of hot, moisture-laden air which is removed from the mixing chamber through an outlet duct 102 connected to an exhaust plenum 104 mounted on a cover or hood 106 which encloses the upper end of the mixing chamber. The hood 106 is supported on the rim 32 along the upper edge of the wall structure and is bolted in place for easy removal if desired. An exhaust fan (not shown) is connected to the exhaust duct 102'to draw out the moisture-laden heated air produced during the cooling process, and the capacity of the fan is slightly greater than the fan 44 so that excess air infiltrating into the mixing chamber will be carried away.

In a customary foundry, the shaking out of finishedcastings from the molds usually proceeds on a haphazard or intermittent basis, and the flow rate of material available from a mold shake-out position in the foundry fluctuates widely and is intermittent. In addition, the temperature and moisture content of the sand in the molds at the time of shake-out often varies widely. The cooling apparatus 10 must be able to compensate for the above-mentioned variables and yet operate on a near continuous basis and provide a finished product having relatively uniform characteristics of temperature and moisture.

The water manifold is supplied from a waterline 108 having a solenoid operated valve 110 for regulating the amount of water introducedto the manifold during timed intervals. Electric current for opening the normally closed water control valve 110 is directed to the valve through a lead 112 connected to a moisture control system (FIGS. 4 and 5). The control system 120 is adapted to continuously sense the moisture content of the material in the mixing chamber and to control valve 110 accordingly. i

In accordance with the present invention, the moisture-control system of the apparatus includes a plurality of electric probes or sensing electrodes for measuring the resistance of the granular material in the mixing chamber 20. Because the sidewall 30 of the mixing chamber 20 is formed of flexible, resilient material, which is also a good electrical insulator, positioning, mounting and placement of the electrodes or probes at the proper positions on the mixing chamber wall to obtain a representative reading are greatly simplified over prior art devices wherein special insulating panels and other components must be used to insulate-the probes from the metallic, conductive mixing chamber walls. One or more pairs of electric probes may be used and the electrodes of each pair are usually mounted on sidewalls opposite one another so that current flow between the pair is generally transverse across the body of material in the mixing chamber.

Referring now, specifically, to FIGS. 2 and 3 of the drawings, a typical electric probe 130 suitable for usein the system and easy mounting on the insulating wall of the mixing chamber is therein illustrated in enlarged detail. The mounting and placement of the probe on the wall of the mixing chamber are simplified by the fact that the chamber wall itself is formed of insulating material and, accordingly, insulating panels, cutouts, or other. apparatus for insulating the probe electrically from a metal wall or framework of the machine is thereby eliminated. The probe 130 includes a circular current carrying disc or washer 132 adapted to seat against the inside face of the insulating wall 30 and a headed pin or terminal bolt 134 is secured to the disc 132 with the stem projecting through the central opening therein and the headed portion welded or otherwise attached to the disc, as best shown in FIG. 2. In order to mount the probe on the mixing chamber sidewall 30 it is only necessary to provide a circular aperture 30a in the wall at the desired location, and a suitable washer 136, tubular spacing sleeve 138, lock washer 140, and a pair of locknuts 142 are provided to hold the probe 130 firmly in place on the wall. The probes or sensing electrodes 130 are mounted adjacent the lower edge portion of the wall, so that the entire surface of the disc 132 will normally be covered by material and an accurate current reading will be obtained even though the total volume of material in the chamber is relatively low. Electrical connection to the sensing electrode is made to the outer threaded end portion of the terminal bolt 134 by means of a socket-type connector lug 144-secured in place on the terminal by a lock washer 146 and nut 148. The lugs 144 are connected to sensing leads 150 positioned in the plenum chamber 40, which serves as a conduit or protective box therefor. Movement of the cooling air in the plenum around the leads 150 maintains the leads at a substantially constant temperature so that no inaccuracies in sensing current, because of the changes in the resistance of the leads due to temperature changes occur. As shown in the block diagram of FIG. 4, two pairs of sensing probes 130 are mounted on opposite sections of the inner wall 30 of the mixing chamber 20 and each pair is provided with a pair of lead wires 150 connected to the moisture controller, although any number of pairs of probes canbe-used to provide extremely accurate sensing of the moisture content of the material. When thematerial in the mixing chamber is relatively wet, the moisture in the material spaced between each pair of sensing probes 130 providesa relatively low resistance current path, and thus current flow between electrodes is considerably larger than when the material is relatively dry. The amount of sensing current flowing in each pair of lead wires 150, connected to the respective pairs of sensing electrodes 130, is thus directly responsive to the moisture content vof the material'and roughly inversely proportional to the temperature. The sensing current flow between the pairs of electrodes is therefore used as a control signal responsive to the sand temperature for the moisture control system, and the system provides an appropriate output current through the lead 112 for operating the control valve 110 for timed intervals to add the desired amount of water to provide the necessary evaporative cooling in the chamber.

From the foregoing, it can be seen that the moisture control system provides a means for regulating the amount of moisture added to the material in the chamber and thus the amount of evaporated cooling is regulated in direct response to the temperature of the material. Even though the flow rate of material introduced into the mixing chamber through the deliverychute l6 is intermittent andfluctuates widely, the final product or finished material leaving the chamber via the dischargeopening 64 is relatively uniform in temperature and moisture content because of the accurate regulation andcontrol of the water added through the manifold 100.

In accordance with the present invention, in order for the probe system sensing means of the moisture controller 120 to function properly, it is necessary that at least enough material be present in the mixing chamber 20 to engage the outer conducting discs 132 of the sensing electrodes 130, and for this purpose a current'sensingtransformer 152 is provided to sense the current drawn by the motor 70 through one of the power supply leads 70a, 70b, and 70c. The current transformer is connected to the moisture controlsystem via leads 154, and operates to disable the moisture control system when the quantity of material in the chamber 20 is insufficient to obtain the desired coverage over the discs 132 of the sensing probes 130. The disabling system is similar in operation to the door control system previously described and a needle E is provided to indicate the amount of material present in the mixing chamber, while a low-set needle D is used to selectively set the minimum level of material needed before the moisture control system will go. into operation. Whenever the amount of material in the mixing chamber is not sufficient to completely cover the faces 132 of the probe 130, the moisture control system is disabled and no moisture will be added through the manifold 100 because the control valve 110 is closed.

The control system includes a remote indicator panel 160 (FIG. 4) having an on" lamp 162 which is illuminated whenever power is supplied to the control system. in addition, the control panel includes a red lamp '170 for indicating that there is insufficient sand in the mixing chamber for operation of the system and an amber lamp 172 indicating that sufficient sand is present for an accurate moisture reading. The control panel also includes an adjustable control 166 movable along a suitable scale 168 by which an operator canadjust and control the desired moisture level setting for the material. Lamp 174 is provided on the control panel to indicate to the operator the moisture condition of the sand or other granular material in the chamber as sensed through the probes 130. The green lamp 174 indicates that the material in the mixing chamber is sufficiently moist, while another lamp 176, preferably of a different color, is illuminated whenever moisture is being added to the sand through the water manifold 100.

. Having reference now to FIG. 5 of the drawings, the control circuit of the moisture controller 120 is illustrated in simplified schematic form. In general, the circuit includes a power supply section generally designated as 180, a material level responsive circuit generally designated as 182, a moisture level sensing circuit 184 and a moisture controlling circuit generally designated as 186. More specifically, and referring first to the power supply section 180, a suitable source of alternating current power is applied to the primary winding of an input transformer 188 through a pair of fuses 190 under the control of a ganged double pole main power switch 192. When the switch 192 is closed, power is applied to a pair of power supply conductors 194 and 196 connected to the secondary winding of the input transformer 188.

As noted above, the moisture controller is automatically disabled unless a predetermined desired amount of material is present within the mixing chamber 20. The material level responsive circuit 182 serves to operate the moisture level sensing circuit 184 and the moisture controlling circuit 186 only when the desired amount of granular material is present. The transformer winding 152 is connected in series with the primary winding of a coupling transformer 198 and the meter indicator E. The secondary winding of the transformer 198 is connected in series with a variable resistance 200 controlled by a manually operated adjustment device and indicator D and with the winding of a relay 202. The relay 202 includes a first set of normally closed relay contacts 202a serving to energize the lamp 170 when insufficient material is present in the mixing chamber 20. A second set of normally open relay contacts 202b are operable for energization of the indicator lamp 172 and for energization of the circuits 184 and 186 when sufficient material is present.

When the level of material in the mixing chamber 20 is increased to the desired level, the current flowing through the secondary circuit of the coupling transformer 198 increases to the level required to operate the relay 202. Opening of the contacts 202a disconnects the circuit for energization of the lamp 170 and closure of the contacts 202k serves to energize the lamp 172 and to energize the primary winding of a transformer 204 which supplies power to the moisture level sensing circuit 184. v

In general, the moisturelevel sensing circuit 184 serves to operate a suitable signal controlled switching device 206 when the moisture content of the mixture in the chamber 20 falls below a selected, desired level. The device 206 may comprise a relay circuit device, a solid state switching circuit device, or the like, and is schematically illustrated in block form as including a pair of switch contacts 208 movable either to an open or closed position. Because many devices and circuits of this type are well known to those skilled in the art and may be used in the illustrated circuit, a further detailed description is not believed to be necessary.

Oneor more pairs of the sensing probes are connected in a bridge circuit together with a variable resistance 210 and a pair of fixed resistances 212. The variable resistance 210 is adjustable by means of the moisture level setting control 166 to the end that the bridge circuit is balanced when the desired level of moisture exists in the material within the mixing chamber 20. The bridge is excited by means of the secondary winding of the transformer 204 when the relay 202 is energized, and the output terminals of the bridge are coupled to the signal controlled switching device 206 and also to a moisture level indicator 214.

When the bridge circuit, including the probes 130, is balanced or is unbalanced in the direction indicating that more than enough moisture is present, the signal controlled switching device 206 remains in the illustrated condition with the switch 208 closed, thus completing a circuit across its output terminals. However-,when the bridge circuit becomes unbalanced in the direction indicating insufficient moisture within the material contained in the chamber 20, the signal controlled switching device 206 is operated to produce an open circuit between its output terminals.

Having reference now to the moisture controlling circuit 186, this circuit serves to operate the water control solenoid valve 110 in response to the operation of the signalcontrolled switching device 206. More specifically, when the demand for moisture is satisfied the circuit 186 maintains the solenoid valve 110 in a closed, deenergized condition. However, when the moisture level sensing circuit 184 indicates a demand for water, the moisture controlling circuit 186 serves to alternately open and close the solenoid valve 1 10 in order to discharge predetermined amounts of water into the mixing chamber until such time as the demand for moisture is satisfied.

Proceeding to a more detailed description of the moisture controlling circuit 186, the circuit includes a main relay 216 having a winding in series with the output terminals of the controlled switching device 206 schematically illustrated as the switch 208. If desired, the relay 216 may be a time delay or timer circuit controlled relay having a pair of normally closed contacts 216a and a pair of normally open contacts 216b, the operation of which follows the energization of the relay winding by a time period, such as one-half second. When the demand for water is satisfied, a circuit for energization of the winding of the relay 216 is completed by operation of the signal controlled switching device 206, and after expiration of the one-half second time delay period, the normally open contacts 216b close in order to energize the indicator lamp 174. in addition, the contacts 216a open, thereby to disable a circuit for producing operation of the solenoid valve 110 and thereby to prevent the addition of water to the material within the mixing chamber 20.

In response to a demand for water, the output terminals of the signal controlled switching device 206 are opened, thereby to discontinue the circuit for energization of the relay 216. At this time, the relay contacts 2161: move to their normally open position, thereby to discontinue operation of the lamp 174. Simultaneous closure of the relay contacts 216a completes a circuit for energization of the winding of a second time delay or timer circuit controlled relay 218. The time delay characteristics of the relay 218 are such that two sets of normally open relay'contacts 218a and 218b move to their closed condition one second after energization of the winding 218. Consequently,one second after deenergization of the relay 216, the normally open contacts 2181) move to their closed position, thereby to complete a circuit for energization of the indicator'lamp 176 and the winding of the solenoid valve 110. As a result, the solenoid valve 110 is moved from its closed to its open condition and water is added to the mixture within the chamber 20.

In order to produce a cycling, or alternately open and closed, operation of the solenoid valve 110 a third time delay relay 220 is provided. This relay includes a normally. closed set of relay contacts 220a in series with the winding of relay 218 as well-as a winding in series with the normally open contacts 218a of the relay 218. The time delay characteristics of the relay 220 are such that its normally closed contacts 220a open two seconds after energization of the relay 220.

Upon operation of the relay 218 in response to a demand for water in the manner described above, when the contacts 218a close a circuit is completed for energization of the wind ing of relay 220. Two seconds thereafter, the contacts 220a of therelay=220 move to their open position, thus discontinuing the energization of relay 218. Consequently, the relay contacts 218b open to discontinue the energization of the lamp 116 and the solenoid valve 110. Simultaneous opening of the contacts 218a discontinues the energization of the winding of relay 220, resulting in rcclosure of contacts 220a. When contacts 220a reclose, relay 218 is once again energizcdand one second later contacts 218a and 218k are reclosed in order to once more add water and to again energize relay 220 to produce further cycling action. Due to the operation of the time delay relays 218 and 220, during an insufficient water condition the solenoid valve 110 is repetitively operated for approximately a 2-second period and is then turned off for approximately'a l-second period, and this cyclical operation continues until such time as the demand for water is satisfied.

Whenever the moisture level of the mixture in the mixing chamber 20 reaches the predetermined desired level, the circuit for energization of the relay 216 is again reestablished by operation of the signal controlswitching device206. After a )-second time delay, the relaycontacts 216a are opened to I open the circuit for energization of the relay 218 and to prevent the addition of additional water. Simultaneously, closure of the relay contacts 216b completes a circuit for energization of the indicating lamp 174.

Reviewing the operation of the control circuit for the moisture controller 120, when the main switch 192 is closed and when sufficient material is present in the mixing chamber to cause the material level responsive circuit 1'82 to operate the relay 202, the moisture level sensing circuit! 184 operates the moisture controlling circuit 186 to maintain the desired amount of moisture within the mixture. When the resistance exhibited between one or more sets of probes 130 is at a low level indicating sufficient moisture, the signal controlled switching device 206 serves to energize the relay 216 to maintain the lamp 174 in an energized condition and to prevent the addition of water. Alternatively, when the resistance detected between one or more sets of probes 130 rises to a high level, indicating absence of sufficient water, the relay 216 is deenergized and water is added to the mixture by alternately opening and closing the solenoid valve through operation of the time delay relays 218 and 220. I

It will be seen from the foregoing that the present invention provides a continuous system for cooling foundry sand or other granular material which is supplied on an intermittent basis or at a widely fluctuating flow rate. The system provides uniformity in temperature and moisture content of the finished product discharged from the system even though the incoming material varies widely in temperature and moisture content. The moisture control system of the invention is automatically taken out of operation any time there is not sufficient material in the mixing chamber to obtain an accurate sensing current through the material between the sensing probes 130. The sensing probes are easily mounted directly on the insulating inner wall 30 of the mixing chamber in the most suitable position in the mixing chamber for obtaining accurate and truly representative moisture sensing information and, moreover, no costly and complicated insulating panels or mounting frames for the sensing probes are required. The moisture control system, in combination with the automatic door control, provides a continuously operating cooling system which is effective and accurate even though wide fluctuations in material temperature and moisture content and wide fluctuations in flow rate of material into the system are present. The finished product is relatively uniform in temperature and moisture content even though the above fluctuations are present in material fed into the system.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A continuous system for cooling hot granular material comprising a treatment chamber having an upwardly extended sidewall formed of electrically insulating material and an inlet and an outlet, means for moving said material from said inlet toward said outlet during the cooling process, water supply means for adding moisture to said material in said chamber for cooling the same and control means for regulating 'said water supply means continuously to maintain a desired level of moisture content in said material and including at least one pair of electrodes'mounted on said insulating sidewall for passing current through said wetted material in said chamber, said control means including a bridge circuit coupled to said electrodes, said bridge circuit being constructed and arranged to reach a predetermined state of unbalance in response to said moisture content falling below said desired level, switch means continuously coupled to said bridge circuit for operation from a first condition to a second condition only during said predetermined state of unbalance, time delay relay means coupled to said switch means for operating said water supply means only in response to said switch means remaining in said second condition for a substantial period of time, means normally operating to excite said bridge circuit, and means responsive to the level of material in said chamber for disabling said exciting means in response to a predetermined decrease in the level of material.

2. The system of claim 1 wherein said insulating sidewall is provided with perforations for said electrodes, each of said electrodes comprising a flat current disc of substantial area disposed on the inside surface of said sidewall for contact with the material and a pin secured to said disc and extending through a perforation outwardly of the opposite sidewall.

3. The system of claim 2 including a plenum chamber outwardly of said sidewall and opening defining means in said sidewall for directing fluid in said plenum chamber directly 

1. A continuous system for cooling hot granular material comprising a treatment chamber having an upwardly extended sidewall formed of electrically insulating material and an inlet and an outlet, means for moving said material from said inlet toward said outlet during the cooling process, water supply means for adding moisture to said material in said chamber for cooling the same and control means for regulating said water supply means continuously to maintain a desired level of moisture content in said material and including at least one pair of electrodes mounted on said insulating sidewall for passing current through said wetted material in said chamber, said control means including a bridge circuit coupled to said electrodes, sAid bridge circuit being constructed and arranged to reach a predetermined state of unbalance in response to said moisture content falling below said desired level, switch means continuously coupled to said bridge circuit for operation from a first condition to a second condition only during said predetermined state of unbalance, time delay relay means coupled to said switch means for operating said water supply means only in response to said switch means remaining in said second condition for a substantial period of time, means normally operating to excite said bridge circuit, and means responsive to the level of material in said chamber for disabling said exciting means in response to a predetermined decrease in the level of material.
 2. The system of claim 1 wherein said insulating sidewall is provided with perforations for said electrodes, each of said electrodes comprising a flat current disc of substantial area disposed on the inside surface of said sidewall for contact with the material and a pin secured to said disc and extending through a perforation outwardly of the opposite sidewall.
 3. The system of claim 2 including a plenum chamber outwardly of said sidewall and opening defining means in said sidewall for directing fluid in said plenum chamber directly into the material for cooling the same and evaporating the moisture therefrom.
 4. The system of claim 3 including conductor means in said plenum chamber connected to said pins of said electrodes.
 5. The continuous system of claim 4 including movable door means for controlling the flow of material from said chamber through said outlet, and means responsive to the load on said motor driven means for regulating the movement of said door means to maintain a selected level of material in said chamber. 